Not necessarily, but this is not a license to open up your tolerance for gage variations. An absolutely dead-flat gage and weight profile is usually the best answer. Winders may object to profile variations so small that they escape the best test-lab measures. This is especially critical for webs that are distorted by stretching over gage bands to cause baggy lanes, as well as for winders which use or require nips, such as layon rollers or surface winders.

In fact, the fussiest customer for a flat web is almost always your winder rather than your test lab or end-user customer. The most sensitive measure of a flat profile is a wound roll that is flat. In other words, what most people call roll build problems are in fact manufacturing profile problems. Every effort must be made to improve communication from converting to manufacturing.

The challenge, however, is that the feedback delay is much longer from customers than from the test lab to manufacturing. The test lab will usually get results before the next master roll is finished. The winder, however, may be running material that was made days, weeks or even months ago. Also, (winder) customer feedback is usually qualitative rather than quantitative.

Hints of manufacturing problems are easy to see if you look closely. For example, a star on both ends of a roll might be either a web or a winding problem. However, a star on only one end of a roll is almost certainly a web problem. Telescoping that strongly favors one direction is another hint of gage variation. Defects that move from one CD location to another are a strong clue to profile variation. Narrow bands are another clue for profile problems. There are a few cases, however, where flat is not always the best answer.

Air Handling: Air will be entrained if you are winding a smooth product (such as film or some paper) at very high speeds. If too much air is entrained, roll edge quality may suffer. In smooth thin film, buckles may form later as air escapes from rolls and allows the roll to collapse. In these cases, the best profile may be a hint of a convex football shape. Even so, the best profile is probably so flat that you wouldn’t even be able to measure the ends being low with typical instruments.

Wrinkle-Prone Rolls: A very few rolls would benefit from a tiny concave shape. These cases would often be tacky low-modulus products wound without a nip. The concave shape turns the wound roll itself into a “concave spreader roll.”

Traction: Another, very rare, application for a tiny concave shape might be to nail the edges of the wound roll layers to each other so that the roll can be built without offsets and telescopes.

Bumpy: There are a few defects on special products where dead flat does not wind well. The only ones I have seen are rare cases involving film.

Even though there are cases where dead flat is not always best, this does nothing to relieve the challenges of manufacturing. To do a decent job on a mild football shape, for example, is far more difficult than mere flat, which already escapes most of us.

920/725-7671 drroisum@aol.com, www.roisum.com